The present invention relates to a semiconductor storage device, and more particularly to a dynamic semiconductor storage device.
In the dynamic semiconductor storage device, a reduction in circuit area is an important task. As a method of reducing the circuit area, there has been known a technique in which a coupling destination diffusion layer having a switch that column-selects signals output from sense amplifiers of a folding bit line system is shared by repetition of an array structure.
FIG. 1 is a layout diagram illustrating a semiconductor layout of open bit sense amplifiers in a general semiconductor memory device. The semiconductor layout of the sense amplifiers in FIG. 1 will be described.
The layout diagram of FIG. 1 illustrates first to fourth sense amplifiers SA1 to SA4, first to fourth bit lines BL1 to BL4, first to fourth dummy bit lines DBL1 to DBL4, first and second word lines WL1 and WL2, first and second dummy word lines DWL1 and DWL2, first to eighth memory cells MC1 to MC8, and first to eighth dummy cells DC1 to DC8.
In a lateral direction of FIG. 1, the first to fourth bit lines BL1 to BL4 and the first to fourth dummy bit lines DBL1 to DBL4 are arranged in parallel. In this example, the first dummy hit line DBL1 is arranged on an extension of the first bit line BL1. Likewise, the second to fourth dummy bit lines DBL2 to DBL4 are arranged on extensions of the second to fourth bit lines BL2 to BL4, respectively.
In a direction orthogonal to the first to fourth bit lines BL1 to BL4 and the first to fourth dummy bit lines DBL1 to DBL4, that is, in a longitudinal direction of FIG. 1, the first and second word lines WL1 and WL2, and the first and second dummy word lines DWL1 and DWL2 are arranged in parallel.
The first to fourth sense amplifiers SA1 to SA4 are arranged in a matrix between the first and second word lines WL1 and WL2, and the first and second dummy word lines DWL1 and DWL2. That is, the first and second sense amplifiers SA1 and SA2 are arranged on extensions of the first and second bit lines BL1 and BL2, and the first and second dummy bit lines DBL1 and DBL2, so as to be adjacent to each other in a direction of the extension. Likewise, the third and fourth sense amplifiers SA3 and SA4 are arranged on extensions of the third and fourth bit lines BL3 and BL4, and the third and fourth dummy bit lines DBL3 and DBL4, so as to be adjacent to each other in a direction of the extension. The first to third sense amplifiers SA1 and SA3 are arranged adjacent to each other in a direction of the first and second word lines WL1 and WL2. Likewise, the second and fourth sense amplifiers SA2 and SA4 are arranged adjacent to each other in a direction of the first and second word lines WL1 and WL2.
The first to eighth memory cells MC1 to MC8 are arranged in a matrix at intersections of the first to fourth bit lines BL1 to BL4, and the first and second word lines WL1 and WL2. In this example, the first to fourth memory cells MC1 to MC4 are arranged at the intersections of the first word line WL1, and the first to fourth bit lines BL1 to BL4, respectively. Also, the fifth to eighth memory cells MC5 to MC8 are arranged at the intersections of the second word line WL2, and the first to fourth bit lines BL1 to BL4, respectively.
Likewise, the first to eighth dummy cells DC1 to DC8 are arranged in a matrix at intersections of the first to fourth dummy bit lines DBL1 to DBL4, and the first and second dummy word lines DWL1 and DWL2. In this example, the first to fourth dummy cells DC1 to DC4 are arranged at the intersections of the first dummy word line DWL1, and the first to fourth dummy bit lines DBL1 to DBL4, respectively. Also, the fifth to eighth dummy cells DC5 to DC8 are arranged at the intersections of the second dummy word line DWL2, and the first to fourth dummy bit lines
The first sense amplifier SA1 has one end coupled to the first bit line BL1, and the other end coupled to the first dummy bit line DBL1. Likewise, the second to fourth sense amplifiers SA2 to SA4 have one ends coupled to the second to fourth bit lines BL2 to BL4, and the other ends coupled to the second to fourth dummy bit lines DBL2 to DBL4, respectively.
The first word line WL1 is coupled to the first to fourth memory cells MC1 to MC4. The second word line WL2 is coupled to the fifth to eighth memory cells MC5 to MC8. Likewise, the first dummy word line DWL1 is coupled to the first to fourth dummy cells DC1 to DC4. The second dummy word line DWL2 is coupled to the fifth to eighth dummy cells DC5 to DC8.
The first bit line BL1 is coupled to the first and fifth memory cells MC1 and MC5. The second bit line BL2 is coupled to the second and sixth memory cells MC2 and MC6. The third bit line BL3 is coupled to the third and seventh memory cells MC3 and MC7. The fourth bit line BL4 is coupled to the fourth and eighth memory cells MC4 and MC8.
Likewise, the first dummy bit line DBL1 is coupled to the first and fifth dummy cells DC1 and DC5. The second dummy bit line DBL2 is coupled to the second and sixth dummy cells DC2 and DC6. The third dummy bit line DBL3 is coupled to the third and seventh dummy cells DC3 and DC7. The fourth dummy bit line DBL4 is coupled to the fourth and eighth dummy cells DC4 and DC8.
The first to fourth bit lines BL1 to BL4 communicate information charge with the first to eighth memory cells MC1 to MC8. Likewise, the first to fourth dummy bit lines DBL1 to DBL4 communicate information charge with the first to eighth dummy cells DC1 to DC8.
Any one of the first and second word lines WL1 and WL2 is selected to conduct the selection of the first to eighth memory cells MC1 to MC8. In this situation, likewise, any one of the first and second dummy word lines DWL1 and DWL2 is selected to conduct the selection of the first to eighth dummy cells DC1 to DC8.
In this example, any memory cell is arranged at all of the intersections between the first to fourth bit lines BL1 to BL4, and the first and second word lines WL1 and WL2. Likewise, any dummy cell is arranged at all of the intersections of the first to fourth dummy bit lines DBL1 to DBL4, and the first and second dummy word lines DWL1 and DWL2. That is, a configuration of the bit lines corresponding to the cell array is of an open type.
Each of the first to eighth memory cells MC1 to MC8 is configured by one transistor and one capacitor. Each of those memory cells stores binary data of one bit as charging and discharging states of the capacitor therein, and inputs and outputs the data through the transistor selected by the bit line and the word line coupled to two terminals thereof.
FIG. 3 is a block diagram illustrating wiring for a BUS signal, a dummy bus signal, and a column select signal in the sense amplifiers in a simplified layout diagram of FIG. 1. The block diagram of FIG. 3 illustrates a first memory cell array MCA1, a second memory cell array MCA2, a first sense amplifier circuit SA1, a second sense amplifier circuit SA2, a first bit line BL1, a second bit line BL2, a first dummy bit line DBL1, a second dummy bit line DBL2, a first column select signal line YSW1, a second column select signal line YSW2, a bus line BUS1, and a dummy bus line DBUS1.
In the block diagram of FIG. 3, the first memory cell array MCA1 corresponds to the first, second, fifth, and sixth memory cells MC1, MC2, MC5, and MC6 in FIG. 1. The second memory cell array MCA2 corresponds to the first, second, fifth, and sixth dummy cells DC1, DC2, DC5, and DC6 in FIG. 1. The first sense amplifier circuit SA1, the second sense amplifier circuit SA2, the first bit line BL1, the second bit line BL2, the first dummy bit line DBL1, and the second dummy bit line DBL2 are denoted by the same symbols in FIGS. 1 and 2.
FIG. 2 is a circuit block diagram schematically illustrating an internal configuration of the first sense amplifier circuit SA1 in FIG. 3. Referring to FIG. 2, the first sense amplifier circuit SA1 includes a sense amplifier SA, an equalizer circuit EQ, and a transfer circuit DQ. The transfer circuit DQ includes a first transistor DQT1 and a second transistor DQT2.
The first column select signal line YSW1 is coupled to the first sense amplifier circuit SA1. Similarly, the second column select signal line YSW2 is coupled to the second sense amplifier circuit SA2 (not shown in FIG. 2). The first bit line BL1 and the first dummy bit line DBL1 are coupled to the first sense amplifier circuit SA1. The second bit line BL2 and the second dummy bit line DBL2 are coupled to the second sense amplifier circuit SA2.
In the first sense amplifier circuit SA1 of FIG. 2, the first bit line BL1 is commonly coupled to one end of the sense amplifier SA, one end of the equalizer circuit EQ, and one of a source and a drain of the first transistor DQT1 in the transfer circuit DQ. The first dummy bit line DBL1 is commonly coupled to the other end of the sense amplifier SA, the other end of the equalizer circuit EQ, and one of a source and a drain of the second transistor DQT2. The bus line BUS1 is coupled to the other of the source and the drain of the first transistor DQT1. The dummy bus line DBUS1 is coupled to the other of the source and the drain of the second transistor DQT2 in the transfer circuit DQ. The first column select signal line YSW1 is commonly coupled to gates of the first and second transistors DQT1 and DQT2 in the transfer circuit DQ.
Referring to FIGS. 2 and 3, the operation of the sense amplifier circuit in a related art will be described. First, the sense amplifier SA determines values of the respective signals that are transmitted through the first bit line BL1 and the first dummy bit line DBL1. Then, the first column select signal line YSW1 transmits the respective signals decided by the first bit line BL1 and the first dummy bit line DBL1 toward an external circuit through the bus line BUS1 and the dummy bus line DBUS1. Thereafter, the signals transmitted through the bus line BUS1 and the dummy bus line DBUS1 are amplified by a downstream circuit. Accordingly, a difference in signal capacity between the bus line BUS1 and the dummy bus line DBUS1 needs to be reduced as much as possible. This is because the large difference in the signal capacity may cause a malfunction or a speed delay in the downstream circuit.
FIG. 4A is a circuit diagram illustrating a portion relating to the first to fourth transfer circuits DQ1 to DQ4 in the first to fourth sense amplifiers SA1 to SA4, extracted from the semiconductor memory device of FIG. 1. The circuit diagram of FIG. 4A includes first to fourth transfer circuits DQ1 to DQ4, first to fourth column select signal lines YSW1 to YSW4, the first to fourth bit lines BL1 to BL4, the first to fourth dummy bit lines DBL1 to DBL4, the bus line BUS1, and the dummy bus line DBUS1. The first transfer circuit DQ1 includes a first transistor DQ1T1 and a second transistor DQ1T2. The second transfer circuit DQ2 includes a first transistor DQ2T1 and a second transistor DQ2T2. The third transfer circuit DQ3 includes a first transistor DQ3T1 and a second transistor DQ3T2. The fourth transfer circuit DQ4 includes a first transistor DQ4T1 and a second transistor DQ4T2.
The first column select signal line YSW1 is commonly coupled to the respective gates of the first and second transistors DQ1T1 and DQ1T2 in the first transfer circuit DQ1. The first bit line BL1 is coupled to one of a source and a drain of the first transistor DQ1T1 in the first transfer circuit DQ1. The first dummy bit line DBL1 is coupled to one of a source and a drain of the second transistor DQ1T2 in the first transfer circuit DQ1.
Likewise, when an index i is generalized as any one of integers 2 to 4, an i-th column select signal line YSWi is commonly coupled to the respective gates of first and second transistors DQiT1 and DQiT2 in an i-th transfer circuit DQi. An i-th bit line BLi is coupled to one of a source and a drain of the first transistor DQiT1 in the i-th transfer circuit DQi. An i-th dummy bit line DBLi is coupled to one of a source and a drain of the second transistor DQiT2 in the i-th transfer circuit DQi.
The bus line BUS1 is commonly coupled to the other of the source and the drain of the respective first transistors DQ1T1 to DQ4T1 in the first to fourth transfer circuits DQ1 to DQ4. The dummy bus line DBUS1 is commonly coupled to the other of the source and the drain of the respective second transistors DQ1T2 to DQ4T2 in the respective first to fourth transfer circuits DQ1 to DQ4.
FIG. 4B is a plan view illustrating a semiconductor layout according to the circuit diagram of FIG. 4A. Each of the first and second transistors DQ1T1 to DQ4T1 and DQ1T2 to DQ4T2 in the respective first to fourth transfer circuits DQ1 to DQ4 is drawn as a diffusion layer and a gate formed on the diffusion layer. In this example, portions of the diffusion layer on both sides of the gate in each transistor operate as the source and the drain. Also, the first to fourth column select signal lines YSW1 to YSW4 are drawn as wires that couple the gates of the two transistors.
FIG. 4C is a plan view illustrating a semiconductor layout in which the semiconductor layout of FIG. 4B is improved to share the diffusion layers of partial transistors. The semiconductor layout of FIG. 4C is equivalent to the semiconductor layout of FIG. 4B which is modified as follows. That is, a positional relationship of the first and second transistors DQ1T1 and DQ1T2 in the first transfer circuit DQ1 is first horizontally reversed. Further, a positional relationship of the source and the drain of each of the first and second transistors DQ1T1 and DQ1T2 in the first transfer circuit DQ1 is horizontally reversed. Then, the diffusion layer of one of the source and the drain of the first transistor DQ1T1 in the first transfer circuit DQ1, which is coupled to the bus line BUS1, and the diffusion layer of one of the source and the drain of the first transistor DQ2T1 in the second transfer circuit DQ2, which is coupled to the bus line BUS1, are integrated with each other. As a result, the first transistor DQ1T1 in the first transfer circuit DQ1 and the first transistor DQ2T1 in the second transfer circuit DQ2 are configured so that two gates are formed in one diffusion layer.
Likewise, a positional relationship of the first and second transistors DQ3T1 and DQ3T2 in the third transfer circuit DQ3 is first horizontally reversed. Further, a positional relationship of the source and the drain of each of the first and second transistors DQ3T1 and DQ3T2 in the third transfer circuit DQ3 is horizontally reversed. Then, the diffusion layer of one of the source and the drain of the first transistor DQ3T1 in the third transfer circuit DQ3, which is coupled to the bus line BUS1, and the diffusion layer of one of the source and the drain of the first transistor DQ4T1 in the fourth transfer circuit DQ4, which is coupled to the bus line BUS1, are integrated with each other. As a result, the first transistor DQ3T1 in the third transfer circuit DQ3 and the first transistor DQ4T1 in the fourth transfer circuit DQ4 are configured so that two gates are formed in one diffusion layer.
The semiconductor layout of FIG. 4C obtained by improving the semiconductor layout of FIG. 4B as described above is reduced in dimension in the lateral direction of the drawing so that a circuit area can be saved. On the other hand, there arises such a problem that a difference in capacity between the bus line BUS1 and the dummy bus line DBUS1 is increased as with a total area of the diffusion layers coupled with the respective lines.
In association with the above description, Japanese Unexamined Patent Application Publication No. Hei 7 (1995)-254650 discloses a technique pertaining to a dynamic semiconductor storage device. The dynamic semiconductor storage device in Japanese Unexamined Patent Application Publication No. Hei 7 (1995)-254650 includes a plurality of dynamic memory cells, a plurality of bit lines, a plurality of word lines, and sense amplifier blocks. In this configuration, the dynamic memory cells are arranged two-dimensionally. The bit lines communicate information with those memory cells. The word lines are arranged across those bit lines, and select the memory cells for extracting the information to the bit lines. In each of the sense amplifier blocks are arranged the sense amplifier coupled to the bit line and an equalizer circuit that equalizes the bit line in order to detect and amplify the information in the memory cell, which is extracted to the bit line. In the dynamic semiconductor storage device, a plurality of the sense amplifier blocks is arranged adjacent to each other in a direction of the bit lines. The bit line having another sense amplifier block existing between the bit line and a given sense amplifier block to be coupled is coupled with a wiring layer different from the wiring layer configuring the bit lines. This wiring layer passes through the another sense amplifier, and is coupled to the given sense amplifier block.
Also, Japanese Patent No. 3004177 discloses a technique pertaining to a semiconductor integrated circuit device. The semiconductor integrated circuit device of Japanese Patent No. 3004177 includes column gates each having a first circuit element, and sense circuits each having a second circuit element. In this example, the first and second circuit elements are integrated in the same pattern with each other. In the semiconductor integrated circuit device, each of the column gates includes at least a first transistor disposed in an element area of a semiconductor substrate as the first circuit element. Each of the sense circuits includes at least a second transistor having a common node with the first transistor disposed in the element area as the second circuit element.
Also, Japanese Unexamined Patent Application Publication No. 2004-348934 discloses a technique pertaining to the memory cell. The memory cell of Japanese Unexamined Patent Application Publication No. 2004-348934 includes a first transistor, and a magnetoresistive element. In this example, the first transistor includes a first gate, a first terminal as one terminal thereof other than the first gate, and a second terminal as the other terminal thereof. The magnetoresistive element has a spontaneous magnetization whose magnetization direction is reversed according to stored data, and includes a third terminal as one terminal thereof, and a fourth terminal as the other terminal thereof. The first terminal is coupled to the first bit line. The second terminal is coupled to the second bit line. The first gate is coupled to the first word line. The third terminal is coupled to the second work line. The fourth terminal is coupled to the second terminal.